'Strongholds' in the Bible

Therefore, I will bring the worst of the [Gentile] nations, and they will take possession of their houses [those of the people of Judah]; I will also silence their pride, and their holy places will be profaned.

‘He destroyed their palacesAnd he flattened their cities;And the land and all who were in it were appalledBy the sound of his roaring.

‘They put him in a cage with hooks and chainsAnd brought him to the king of Babylon;They brought him in hunting netsSo that his voice would be heard no moreOn the mountains of Israel.

You shall say this to them, ‘Thus says the Lord God, “As I live, those who are in the ruins certainly will fall by the sword, and I will give whoever is in the open field to the [predatory] animals to be devoured, and those who are in strongholds and in caves will die of virulent diseases.